The need to prevent childhood obesity extends down to our youngest children. Obesity and excessive weight gain in the first year of life are independently associated with higher blood pressure, recurrent wheezing, higher hospital admission rates, and other adverse physical and psychosocial health conditions in childhood. Thus, effective approaches to obesity prevention in early childhood are needed. Because nearly two-thirds of U.S. children under 6 years of age are routinely cared for outside of the home, organized child care is an important setting for obesity prevention. Recent studies suggest that children who attend child care are more likely to be obese than children cared for at home by a parent or other caregiver, and younger children might be most at risk. Our own research found that infants who spent time in child care during the first 6 months of life were heavier at one yea and still heavier at 3 years of age than children cared for at home. These previous studies identified a relationship between child care and obesity, but failed to pinpoint specific causal pathways. The proposed longitudinal study will examine factors contributing to the development of obesity that may be influenced by the child care setting, including dietary behaviors, physical activity and inactivity, stress, and sleep duration and quality. To accomplish these aims, we propose a diverse southern cohort of 800 black, white, and Latino/a infants in various child care arrangements, followed regularly from birth to 12 months of age. Frequent in-home assessments throughout infancy will help pinpoint exactly when children begin to gain weight excessively and will identify risk factors related to energy intake, energy expenditure, stress, and sleep associated with obesity. To mitigate participant burden and enhance retention, we will use Interactive Voice Response (IVR) technology to supplement in-person visits through innovative telephone-administered assessments with parents and child care providers. Results of this study will provide new information on the relationship between child care attendance and obesity and may help determine causality in instances where the associations between these variables have been unclear. Findings will inform state and federal policy governing child care settings and will also guide intervention efforts to help prevent obesity in young children in chil care.